Back flow preventer



Original Filed Nov. 7, 1944 s sheets-sh et 1 June 30, 1959' I T. A. GLASS BACK FLOW PREVENTER 3 Sheets-Sheet 2 47 Original Filed Nov. 7, 1944 Jun 30, 1959 GLASS I 2,892,464

BACK FLOW PREVENTER Original Fi led Nov. 7, 1944 5 Sheets-Sheet 3 United States Patent BACK FLOW PREVENTER Thomas A. Glass, Los Angeles, Calif; Ann Thesiug Glass, executrix of said Thomas A. Glass, deceased, assignor of one-half to Harry H. Glass, Los Angeles, Calif.

Original application November 7, 1944, Serial No. 562,304, now Patent No. 2,654,388, dated October 6, 1953. Divided and this application September 9, 1953, Serial No. 382,112

8 Claims. (Cl. 137-116) This application is a division of Serial 562,304, filed November 7, 1944, now Patent 2,654,388 issued October 6, 1953.

This invention relates to back-flow preventers and has for its principal object the provision of a simple and eificient device of this nature which will prevent contaminationof themain supply when the inlet pressure drops below the outlet pressure, as, for example, when an emergency demand, such as might occur with an extensive fire, might rob the water mains of their normal pressure. I i

A prime object of the invention is to provide a back flow preventer which will have one or more of the following features which define it over the somewhat similar devices of the prior art: (a) The outlet pressure controls the opening and the closing of the inlet closure; (b) The opening and the closing of the inlet closure is goverened by outlet pressure exerted on an area of the inlet closure; (0) The portion of the inlet closure which is exposed to the outlet pressure is rigidly secured to the portion of the inlet closure which is not exposed to the outlet pressure; (d) The outlet pressure and the inlet pressure simultaneously act on a single closure element in opposite directions; (e) The inlet closure and the outlet closure are flexibly connected together to form a single closure element sealing the central zone from the inlet and outlet chambers; (f) A single closure element first opens the inlet seat and then the outlet seat, and, in closing, closes the outlet seat and finally seals the inlet from. the central zone and the outlet; (g) The central zone isso located as always to be filled with water, and the water is at atmospheric pressure when there is no flow, and (h) there are two spaced valves at opposite ends of the central zone and these are constrained to move as a unit so the inlet valve may never leave its seat unless the outlet valve opens at the same time, and hence the inlet valve is governed by the outlet pressure and the valve assembly is subject on one side to the inlet pressure aud on the opposite side to the outletpressure.

Other important features of the invention are the minimizing of head loss in back flow preventers where the pressure in the central. zone is atmospheric when there is no flow, the maintenance of a constant pressure drop or differential thru the valve at all rates of flow whereby the relief valve may be kept closed when either or both seats are uncovered, and the provision of a simple and efiicient device of this kind in which the central zone pressure may be kept equal to, or lower than, the inlet pressure at all times, and be at atmospheric pressure when the central zone' is sealed from both the inlet and the outlet chambers.

A still further object of the invention is to provide a device of this kind in which a signal will be given in case an obstruction should prevent the valve from closing, in which case the water main will be protected, but the consumers supply will leak thru the open valve until the trouble has been corrected. a

. Aside from the fire pumps robbing the main, there are ring.

- a plug 18 having an inserted rubber bumper 19 acting ice a number of other causes of back flow, including heavy demands for water during dry weather in the summer, the reverse pressure due to tanks on tops of tall buildings and filled thru check-valves by pumps on the premises, and the frequent increase in building along a street where the original street main was properly designed but is no longer of sufiicient size to maintain the required pressure during peak loads. The avoidance of back flow hasteceived much study and late last year the Ofiice of Scientific Research and Development considered recommendations that all back fiow preventers which operate under pressure shall have a central zone; that this central zone be provided with a relief device to open the central zone to the atmosphere such that leakage up to 20% of the full open capacity of the preventer on the unpotable side would be carried to atmosphere; that the head loss thru the device will bewithin the Board of National Fire Underwriters requirements; and, in addition, that the device shall meet one of the following requirements:

(1) Pressure on the central zone shall not, when no new exists, exceed more than 3 lbs. the pressure on the potable side., T

.(2) Pressure on the centralzone shall at all times be maintained 'at equal or less than the pressure on the potable side. i

(3) Pressure on the central zone shall at all times be maintained at 2 lbs. less than the pressureon the potable side.

(4) Pressure on the central zone when no flow exists shall be at atmospheric pressure.

It is an object of this invention to provide a device meeting the fourth requirement, this being the hardest to meet, while keeping the head loss within permissible limits. As far as I know, no other back flow preventer has been built having these two features.

In the drawings: 4

Figure 1 is a central vertical section thru the valve.

Fig. 2 is a section on line 2-2, Fig. 1.

Fig. 3 is a section on line 3-3 of Fig. 1.

Fig. 4 is a central section thru the relief valve.

Fig. 5 is-a vertical section through the axis of the main valve.

Figs. 6 and 7 show the device in full open and in nearly closed positions, respectively.

Figs. 8 and 9 show modified forms of the disk and Fig. 10 shows a modified valve.

In Fig. l is shown my preferred form of back flow preventer, including a main valve body 10 thru which fluid passes from the inlet 11 to the outlet 12, past a check valve 15 which is closed during periods of no flow and whenever the outlet pressure equals or exceeds the. inlet pressure. .In keeping with the suggested require ments the relief valve 16 is of a capacity to discharge up to one-fifth of the normal flow in case of leakage into the main valve body. This relief valve 16 is acted upon by opposed pressures of the inletand outlet sides of the main valve. seems from the figure that the diaphragms 60 and 65 are of the same size, there is a very slight difierence and the diaphragm 65 has a slightly greater area. since the outlet pressure is exerted upon a larger area than is the inlet pressure, the relief valve 16 will be opened to the atmosphere whenever the two opposing pressures are equal in head or in pounds per square inch. The diiference in area is very slight, for example, in the I 4 size the diaphragm 60 which is subject to the inlet pressure, would be 4" in diameter and theoutlet ilapressure, would normally phragm 65 subject to the outlet be 45%" in diameter. q

The body 10 has an arched cover 17 andmay carry Referring particularly to Fig. 4, whileit Hence,

as a stop for the valve when fully open. The cored passage in the body forms the middle portion of the central zone. Detachably secured to the body 10, as by bolts 21, is a bronze casting 22 having an annular recess 23 forming the inlet section of the central zone bounded by an inner seat 25 and an outer seat 26 preferably 1ying in a single plane, altho the outer seat may extend further into the chamber 27 of the main valve body 10, it being important that the outer seat 26 be closed before the inner seat 25 and opened later so that the central zone is first closed to the outlet water and then closed to the inlet water and that the central zone be opened to the inlet water before being put in communication with the outlet water which may be non-potable, as when the consumer has an emergency tank filled from a nearby steam.

While the bracket 29 might extend from the body, it is more convenient to form this as an extension of the casting 22 so that the entire assembly may be removed as a unit when the top cover 17 is oh. The hinge 30 is in the form. of a. yoke and having widely spaced arms 31 loosely receiving a mounting pin 32 carrying a weight 33 to maintain a pressure drop in excess of two pounds to insure that the difierential relief valve shall stay closed when either or both of the seats are uncovered, that is, that the relief valve be closed at all times when there is a flow in the normal direction thru the main valve.

The extra weight mounting pin 32 may be kept in place by. washers and cap screws.

The valve closure 15 may be of any convenient type and is shown in Fig. l as composed of a disk 36 held by two clamp plates 37 and 38 in engagement with a rubber facing 40 engaging both of the annular seats 25 and 26, and a flexible member 41 which might be of laminated metal, but is preferably of a sheet membrane. The facing40 is secured to the ring 44 as by the clamp ring 45 and the membrane 41 is similarly secured to the ring 44 by the clamp ring 46. Since both 49 and 41 are flexible, the ring 44, which is thicker axially than the disk, has a slight movement axially of the common axis of the disk, ring, and closure. The ring and the disk have engaging shoulders 48 and 49 to limit the outward movement of the disk when the closure starts to open and one or the other of these closure members carries a small annular rubber seal 50 to prevent foreign particles getting into the space between the shoulders 48 and 49 to lessen the relative movement of the disk and ring. The axial pin 51 is threaded at both ends, as shown, but might be integral with either the clamp plate 37 or the nut 52 which engages the washer 53 holding in place the yoke of the hinge 30 and the sleeve 54.

Considering now the differential relief valve 16, the body is of standard construction having a pair of valves 56 and 57 on a common stem 58 which, however, extends thru flexible sheet membranes 59 on opposite sides of the body and is secured at one end to a diaphragm 60 acted upon by the inlet pressure transmitted by pipe 61 leading from a connection 62 near the inlet flange. The other end of the valve stem 58 is secured to a diaphragm 65 acted upon by the outlet pressure transmitted by a pipe 66 leading from a connection 67 near the outlet flange of the main valve body 10. A pipe 70 much larger than pipes 61 and leads from the cored assage 20 to the relief valve inlet 71 so that when the relief'valves'are open the central zone fluid may be discharged thru the relief valve outlet 74, preferably thru a pipe 75 having therein a flow responsive element 76 controlling a ,visual indicator 77 for a slight flow and air audible. indicator 78 for a larger flow so as to notify the'attcndant of abnormal conditions.

7 It is advisable to have the relief valve outlet 74 at a level well above the main line so that the central zone is'always filled'with water, if that be the fluid passing the main valve. By this the draining of the central zone every time there is no flow is avoided and also the relie valve is protected from sand and sediment sifting into it as would occur with the relief valve located beneath the main valve. It is advisable to coat the bodies of the valves with porcelain enamel to avoid corrosion and incrustation.

As a construction refinement to increase the ease of inspection and repairs, the seat and central zone casting 22, together with the disk and ring assembly 15, can be removed from the valve body thru its open top. This can be done by removing the valve body cover 17 and the outside cap screws 21 that hold the seat and central zone casting. A new gasket 24 of suitable sheet material between the casting and the valve body will seal the joint against leakage when the seat casting is secured in place with the holding cap screws. To facilitate the removal of the disk assembly 15 without removing the seat casting 22, the hinge pin 80 can be withdrawn thru the hole 81 oppositethe pin. The disk assembly can then be lifted free of the valve body for inspection or replacement.

In Fig. 10 there are two spring pressed valves 84 and 85 having a common stem 83 and, therefore, acting as a unit. The relief valve 16 as before is governed by opposing inlet and outlet pressures thru pipes 86 and 87 communicating with the inlet chamber 88 and the outlet chamber 89, respectively. The central zone 90 in this type is cylindrical and vents thru the relief valve 16 by the waste pipe 70.

. In Figure 10 the valve 56 is shown as just opening and the valves 84 and 85 are shown as just closing. As both valves 84 and 85 constantily move as a unit in this modificati'on, a drop in the city pressure is reflected by a drop in pressure in pipe 86 so that the pressure in pipe 87 immediately opens valve 56. Consequently the two springs instantly snap the connected valves 84 and 85 closed. Water in the closed central zone 90 is trapped there at atmospheric pressure and cannot drain. Furthermore, water in the relief valve body would tend to fill the central zone by gravity if there were vacant space, so the central zone is always filled with water, as obviously it is full when both main valves are open and potable water is passing from inlet chamber 88 to the plant system by way of outlet chamber 89, the relief valve 56 being closed at such time. Therefore no water can escape by passing upward through pipe 70.

The closure 15 is much more eflicient than if the rubber facing 40 were backed by a solid member, as the latter would require too great a drop in outlet pressure before the valve could open. Assuming a 4" size, seats of 4%" and 6%" diameter, and an inlet pressure of 60 pounds, it would necessitate the momentary fall of the outlet pressure to 20 pounds before the flow could start from static pressure. This. naturally would prevent the use of faucets located higher than 46 feet above the main line. But by making the closure in two pieces with the disk 4 inches in diameter, it would necessitate the momentary fall of outlet pressure to 47 /2 pounds to raise the disk off its seat. When the outer seat only is closed and the outlet pressure is 47 pounds, the force holding the ring to its seat is only about 200 pounds and the force holding the disk olf its seat is about 196 /2 pounds. The resultant force then, that is holding the ring to its seat, is a force of but 3 /2 pounds. A further drop in pressure of a few ounces will force the ring from its seat and flow will start and these few ounces will continue to hold the close assembly just free of the seats.

We will now consider the operation of the back flow preventer, starting with the position shown in Fig. 7 which illustrates the mechanism as it would appear just after the demand for water had ceased in the house, factory, or other consumers property. With the cessation of flow, the pressure in the body 10 starts to build up. The closure 15, aided by extra weight 33, tends to turn about its pivot 80 on bracket 29 and close flow of water from the'body 10 across the central. zone. The seat 26 is closedprior to the closing of the seat 25 of the inlet pipe, hencethe inlet is still open to the central zone. The chamber 20 and valve 16 are filled, but the relief valve is not yet wasting as the pressure in the body has not quite risen to the point where the greater exposed area of the membrane 65 is able to overcome the lesser area of membrance 60 where the pressure is substantially the inlet pressure, as the flow is so slight. Almost immediately after the first closing of the valve the body pressure reaches the necessary point to overcome the some what higher pressure at the left of the valve 16 so the relief valves 56 and 57 open, as shown in Fig. 7, and this is followed by the complete closure of the valve 15, both of the concentric seats being now engaged by their respective facings, so that no water flows from the inlet or from the outlet. The central zone is then open to atmospheric pressure, as it always is when there is no flow thru the system. This incidentally takes care of any possible leakage from the body and insures that such leakage cannot pass to the main.

Altho the relief valve 16 is open to atmosphere during all periods of no flow, it closes promptly when a faucet is opened in the consumers premises, and remains closed during all of the flow. The demand causes a slight drop in pressure in the body 10. is immediately reflected at chamber 65, so that pressure on the opposite side closes the relief valve. At the same time the pressure of the water on the inlet side of the closure 15 opens this disk assembly in part, water now flowing from the inlet to the central zone building up pressure therein as the water cannot escape as long as the valve 16 is closed. The portion of the disk assembly 15 in rising from the first or inner seat moves to its back position, and in the preferred construction contacts firmly with the shoulder of the outer ring of closure 15. This closure now opens to allow flow from inlet to outlet. The extra weight 33 is so located to cause a higher pressure differential at the angle at which the closure hangs from its pivot 80 when the rate of flow of the water is low. The relief valve is consequently held closed until after the demand for water in the consumers premises has ceased, as just explained.

It is apparent from the above that no back flow can occur normally, as a greater outlet pressure would merely hold the closure all the tighter against its two seats and hold the relief valve in wide open position. Under extraordinary conditions, such, for example, as would occur if a foreign body were caught between the closure and the seats, the relief valve would open wide and its chamber would continuously waste thru pipe 75. This, however, would be indicated, first, by the lamp 77 and then by the bell 78, bringing prompt attention.

In the modified forms shown in Figures 8 and 9 are shown slight modifications of the facing material and the flexible membrane. The form of Fig. 9 is somewhat preferred over that of Fig. 8, and shows the body seats 25 and 26 touching inserted facings 40a of semi-hard rubber composition facing material. In Fig. 8 the facing ma terial 40b is bronze and in this figure the flexible material is of the metallic type as shown at 41b. This is conveniently silver soldered as at 82 at the end of the bend so as to provide the necessary movement.

I claim:

1. In combination, a valve body having an inlet, an outlet, and a central zone communicating with the inlet and the outlet, an inner seat within the body and thou which the inlet fluid passes to the valve body and to the central zone, disk means engaging the inner seat to close the flow between the inlet and the central zone, an outer seat within the valve body and thru which fluid passes to the central zone, ring means engaging the outer seat to close the flow between the central zone and the outlet, a relief valve controlling flow from the central zone and subject to opposing inlet and outlet pressures, said relief valve being located at a level well above the said valve body so that the central zone will always be full of water, and means for flexibly connecting the disk means 6 and the ring means, whereby the disk means opens before the ring means and closes later than the ring means, and the relief valve is always open to atmospheric pressure when the pressure within the valve body is equal to or greater than the pressure on the inlet side of the valve means.

2. The device of claim 1 with signal means controlled by the flow through the discharge side of the relief valve for indicating an above-normal passage of fluid thru the relief valve.

3. The device of claim 2 in which the signal means ineludes one signal for indicating a slight flow and a second signal for indicating a greater flow, said second signal including an audible alarm.

4. The device of claim 1 in which the closure contacting faces of the inner and outer seats are in the same plane, the seat margins are concentric, the disk means and the ring means are pivoted as a uni-t to close the outer and the inner seats in sequence, and the relief valve is biased to open the central zone to atmosphere during periods of no flow.

5. The device of claim 1 in which the area of the closing surface of the disk means is greater than the area of the closing surface of the ring means, whereby the ring means may be held to its seat with a less pressure than is required to hold the disk means against its seat.

6. In a device for preventing flow of non-potable water to a potable supply, a main valve body including an inlet portion, a central zone and an outlet portion, a who between the inlet portion and the central zone, a second valve between the central zone and the outlet portion and directly connected to the first valve, a relief valve connected to the central zone and being located at a higher elevation than the main valve body, a passageway connecting one end of the relief valve with the inlet portion to exert pressure to close the relief valve, a second passageway connecting the opposite side of the relief valve with the outlet portion to exert pressure to open the relief valve when the outlet pressure exceeds the inlet pressure, said relief valve being biased to open the central zone to atmospheric pressure when the central zone is sealed from both the inlet portion and the outlet portion and whereby the central zone pressure never exceeds the inlet pressure.

7. In combination, a valve body having therein two spaced valves forming a central zone between them, means connecting the two valves so that both valves will move together to open or closed position, a relief valve located at a higher level than said valve body, piping connecting the relief valve with the space between the two valves, means for opening the relief valve when thepressure between the two spaced valves is equal to or greater than the pressure upstream of the two valves, and spring means urging the connected valves to closed posi- Hon.

8. The combination with a relief valve body having an entry port and a relief port, a valve movable to close and to open communication between said ports, pressure responsive members on opposite sides of the valve, and means connecting the valve to said members, the members being biased to move the valve to open position when the pressures on the two members are equal; of a main valve body having an outlet port, a central zone, and a potable water inlet; piping connecting the outlet port to one of said pressure responsive members, connecting the potable water inlet to the other pressure responsive member, and connecting the central zone to the entry port of the relief valve body; a one-way valve in the main valve body closing communication between the potable water inlet and the central zone when the pressure in the potable water inlet falls below the pressure at the outlet port, said one-way valve upon falling of pressure at the potable water inlet first closing communication between the central zone and the outlet port and then closing communication between the central zone and the potable water inlet,

References Cited in the file of this patent UNITED STATES PATENTS 8 Dore Feb. 7, 1939 Carlton Nov. 20, 1945 Snydesr Apr. 11, 1950 Snyder Ian. 16, 1951 Griswold Dec. 9, 1952 Rowley July 7, 1953 Griswold July 28, 1953 Glass Oct. 6, 1953 

